Incentivizing customers to refer family and friends as new customers

Hello. I recently began working for a retailer for a large wireless provider. My position is 100% commission. I would like to provide an incentive for customers that have purchased from me to refer family and friends back to me. I was thinking of a few ideas, but I wanted to bounce these off of this community since your probably a lot more experienced in this area than I am. :)

The referral will be earned if my customer refers someone to me and the person they refer activates new service or upgrades their existing phone.

• My initial thought was a gift card to my business. I was thinking $5 or $10. The gift card could be used to make purchases in the store, such as accessories, etc. Also, if they rack up enough referrals, they would have a collection of gift cards to use. I did bounce this idea off an associate and he thought it was a good idea because "...people like something tangible..." The downside to a gift card is that this doesn't require them to do business with me. They can use the gift card with anyone at the store. Also, a gift card to allow purchases of accessories, etc. from my store may not really be a big thing because most people would buy their accessories (phone case, chargers, etc.) when they purchase the phone.
  
• Pay a portion of their phone bill. Maybe $5 or $10 per referral.
  
• Instead of a gift card to my business, I could give a gift card to a local business. I'm in a small town and we do have a few chain businesses, but we also have a few "Mom & Pop" businesses. I was thinking of a local coffee shop. I know the owners and have a good relationship with them, but me giving gift cards to their business will be benefiting their business and not mine.

With all of the above I was also thinking of limiting it to a certain period, such as ".... maximum of x gift cards per y days (30, 60, 90, 180, or something like that).

I am open to your feedback.

Thank you.